The present invention relates to a method of manufacturing a curved profile made of composite material from a rectilinear preform of fiber plies. The invention more particularly relates to a method of manufacturing an aircraft fuselage frame.
According to an embodiment shown in FIG. 1, an aircraft fuselage frame 10 is in the form of a profile having a Z-shaped cross-section whose central portion referred to as a core 12 forms a complete or partial ring. The profile comprises a first wing 14 referred to as an inner wing arranged in the area of the inner edge of the core 12 and perpendicular to the latter and a second wing 16 referred to as an outer wing arranged in the area of the outer edge of the core 12, also perpendicular to the latter.
A method of manufacturing such a composite material frame is described in document FR-2.928.295.
According to this document, first, a substantially rectangular strip is made by stacking on top of one another three plies of pre-impregnated fibers, each ply having fibers oriented along a direction, the strip comprising plies with different fiber orientations, a ply with fibers at 30°, a ply with fibers at 90° and another ply with fibers at 150°.
Then, the strip of fiber plies is arranged on a mandrel made of deformable material, then compressed on this mandrel so as to conform to the shape thereof.
The deformable mandrel is capable of changing shape between a rectilinear position and a curved position but presents an incompressible or quasi-incompressible transverse section.
Subsequently, the deformed strip arranged on the mandrel made of deformable material is placed in contact with a heated tool having, in the periphery thereof, radial sections having a profile complementary to the transverse sections of the mandrel. During bending, the strip is compressed and subjected to an increase in temperature.
Subsequent to the setting in place of this first strip, a second strip of three pre-impregnated fiber plies is cut, then arranged in another deformable mandrel and compressed on the latter.
Then, this second strip deformed on its mandrel made of deformable material is placed in contact with the first strip still in place on the tool, then compressed against the first strip.
To obtain a frame requires, as previously stated, attaching several strips on top of one another before the assembly thus formed is polymerized.
In addition, strips with fibers oriented at 0° can be manually added between certain strips.
This mode of operation is not fully satisfactory for the following reasons:
First, the implementation is relatively long and tedious because the profile is made step by step, a large number of strips having to be deformed and bent successively.
Second, the relative positioning between the strips is difficult to carry out since the strips are constituted of pre-impregnated fibers and cannot easily glide with respect to one another to correct their relative positions. Therefore, it is difficult to ensure that, during bending, the two inner wings of the two strips, the two cores of the two strips, and the two outer wings of the two strips are perfectly in contact with one another over the entire length of the frame. Considering the difficulties of the setting in place, the operators must intervene numerous times to attempt to manually correct the observed defect.
According to another drawback, as the strips are being stacked up, the value of the outer radii increases whereas that of the inner radii decreases, which means that the difference in value between the strip already in place on the bending tool and the attached strip causes a defect referred to as a bridge, the two strips not being closely flattened again one another at the bottom of the radius of curvature. This defect causes, during the polymerization, some undulations that negatively affect the quality of the part.
According to another drawback, it is impossible to bend the strips once they are compacted without causing gliding between the plies of pre-impregnated fibers and thus undulations or wrinkles of fibers.
Finally, the plies of the first strip stay in contact with the tool heated at a temperature on the order of 50° C. much longer than the plies of the last strip attached, which causes the resin impregnating the first plies to age in an accelerated, uncontrolled manner.